The present invention relates to an electromagnetic wave detecting device which is capable of detecting electromagnetic waves including radiation such as x-rays, visible light and infrared light.
Conventionally, known is a two-dimensional electromagnetic wave detecting device in which (a) a semiconductor film which generates an electric charge (an electron-hole pair) by sensing an electromagnetic wave such as X-ray, that is, an electromagnetic wave conductive semiconductor film, and (b) a semiconductor sensor which is made up of pixel electrodes and other elements are disposed in a two-dimensional manner, and in which a switching element is provided on each of the pixel electrodes. In the electromagnetic wave detecting device, the charge is read out column by column by turning on the switching element row by row.
For example, concrete structures and principles of two-dimensional image detecting device which corresponds to the above electromagnetic wave detecting device are disclosed in xe2x80x9cA NEW DIGITAL DETECTOR FOR PROJECTION RADIOGRAFYxe2x80x9d (D. L. Lee, et al., SPIE, 2432, pp.237-249, 1995). Referring to FIG. 9, the principle of the two-dimentional image detector is described below.
The two-dimensional image detecting device has bias electrodes 102 and a plurality of charge collector electrodes 103 which are respectively on upper and lower layers of a semiconductor film 101 made of Se showing electromagnetic wave conductivity. Each of the charge collector electrodes 103 are respectively connected to charge storage capacitor (having a capacitance of Cs) 104 and an active element (TFT) 105. Note that, dielectric layers 106 and 107 as electron blocking layers are provided as needed between the semiconductor film 101 and the bias electrode 102, and between the semiconductor film 101 and charge collector electrode 103, respectively. In addition, 108 indicates an insulating substrate, and the bias electrode 102 is connected to a high voltage power source 109.
When an electromagnetic wave, such as an x-ray, is directed to such a two-dimensional image detecting device, a charge (an electron-hole pair) is generated in the semiconductor film 101. At this stage, the semiconductor film 101 and the charge storage capacitor 104 are serially connected electrically. Therefore, by previously applying a bias voltage to the bias electrode 102, an electron of the charge (electron-hole pair) generated in the semiconductor film 101 moves to a positive (+) electrode side, and a hole moves to a negative (xe2x88x92) electrode side, thereby storing the charge in the charge storage capacitor 104.
By turning on the active element 105, the charge stored in the charge storage capacitor 104 can be taken outside. By (a) thus disposing the charge collector electrode 103, the charge storage capacitor 104 and the active element 105 in a two-dimensional manner, and (b) reading out charges in a line-sequential manner, it becomes possible to obtain two-dimensional information of an electromagnetic wave which is a detection target.
Generally, Se, CdTe, CdZnTe, PbI2, HgI2, SiGe, Si, etc. are used as the semiconductor film 101 which has electromagnetic wave conductivity. Among them, an Se film has a small dark current (a leak current) characteristic and is capable of large-area deposition at a low temperature by vacuum evaporation. For those reasons, the Se film is widely used for the electromagnetic wave detecting device (particularly x-ray detecting device) having a structure in which a semiconductor film 101 is formed directly on an active matrix substrate 110 (see FIG. 9).
As shown in FIG. 10(a) and FIG. 10(b), the two-dimensional electromagnetic wave detecting device using the above-described active matrix substrate 110 has a structure where a driving signal (scanning signal) for driving the active element 105 in a line-sequential manner is inputted from the circumference of the active matrix substrate 110, and each pixel, that is, charges stored in the charge storage capacitor 104 are outputted outside in response to the detection of x-ray (electromagnetic wave). Note that, reference numeral 116 indicates a projection region which is pixel electrode alignment region, shown by a thick line in FIG. 10(b).
The active matrix substrate 110 has scanning lines and readout lines in a lattice manner (usually, matrix of 500xc3x97500xe2x88x923000xc3x973000 pixels). These scanning line and readout line are connected respectively to a signal input terminal 111 and a signal output terminal 112 which are formed in the circumference of the active matrix substrate 110. On the active matrix substrate 110 shown in FIG. 10(a) and FIG. 10(b), the signal input terminals 111 connected to the scanning line are formed along first two sides facing each other (left and right sides), and the signal output terminals 112 connected to the readout line are formed along second two sides facing each other (upper and lower sides).
Further, a gate driver 113 (a driving LSI) is connected to the signal input terminal 111 by a mounting method such as TAB or COG and a readout amplifier 114 which is made up of LSI is connected to the signal output terminal 112 by the same method.
The signal input terminals 111 and the signal output terminals 112 are arranged so as to divide one side into plural divisions corresponding to a plurality of gate drivers 113 (for example, TAB) and readout amplifiers 114 (for example, TAB) connected thereto. For example, in case where TABs for the readout amplifier 114 having 128-channel input terminals are connected with respect to the active matrix substrate 110 having 1536xc3x971536 matrix, twelve TABs per one side are allocated along each side of active matrix substrate 110. Accordingly, it is designed to arrange signal output terminals 112 of the active matrix substrate 110 so as to divide one side into twelve divisions. Further, arrangement of the signal input terminals 111 and the signal output terminals 112 is substantially symmetrical with respect to the center Vo in the vertical direction and the center Ho in the horizontal direction, respectively. Note that, for purpose of explanation, FIG. 10 (a) shows an example that the signal input terminals 111 and the signal output terminals 112 are arranged at four divisions and seven divisions, respectively. In addition, the vertical direction and the horizontal direction are established for purpose of explanation; for example, the directions can be established conversely.
On the other hand, a voltage is applied to the bias electrode 102 from an external power source, that is, a high voltage power source shown in FIG. 9 through a bias supply line 115. Thus, the bias supply line 115 is connected to a connecting section 102a of the bias electrode 102. For limitation of space, the connecting section 102a of the bias electrode 102 is provided in the vicinity of the signal input terminal 111 and the signal output terminal 112.
Incidentally, with respect to the electromagnetic wave detecting device, a high voltage applied to the bias electrode 102 makes it effective to improve the sensitivity for detection of x-ray. Thus, if a-Se film which is capable to form a film easily, for example, is used as a semiconductor film 101 which has electromagnetic wave conductivity, nearly 5000V-15000V of a high voltage can be applied to the bias electrode 102.
However, with respect to the active matrix substrate 110, as described above, in case where the connecting section 102a, to which the bias supply line 115 is connected, of the bias electrode 102 is arranged in the vicinity of the signal input terminal 111 and the signal output terminal 112, application of a high voltage to the bias electrode 102 causes generation of an electrical discharge such as atmospheric discharges and surface creepage between the connecting section 102a and the signal input terminal 111 and between the connecting section 102a and the signal output terminal 112. This might damage the electromagnetic wave detecting device.
An object of the prevent invention is to provide an electromagnetic detecting device with high reliability which can prevent the generation of electrical discharge between a connecting section of a bias electrode and a signal input terminal and between the connecting section and a signal output terminal even if a high bias voltage is applied to the connecting section.
In order to achieve the above object, an electromagnetic wave detecting device of the present invention comprises:
an active matrix substrate including in its circumference signal input terminals and signal output terminals,
a semiconductor film, provided on the active matrix substrate, having electromagnetic wave conductivity, and
a bias electrode, having a connecting section to which a bias supply power source is connected, for applying a bias voltage to the semiconductor film,
wherein at least one of the signal input terminals and the signal output terminals are provided offset so as to be on a side which is away from the connecting section of the bias electrode.
According to this structure, since at least one of the signal input terminals and the signal output terminals are provided offset so as to be on the side which is away from the connecting section of the bias electrode, it is possible to prevent an unnecessary electric discharge such as atmospheric discharge and surface creepage between the connecting section of the bias electrode and at least one of the signal input terminals and the signal output terminals.
That is, the connecting section of the bias electrode to which the bias supply power source is connected is not flat but special in shape. For this reason, even if a molding for insulation is performed, a poor insulation is likely to occur due to cracks in a molded part. As a result, the electric discharge between the connecting section and one of the signal input terminals and the signal output terminals is likely to occur. Therefore, using this structure can prevent the electric discharge between the connecting section and one of the signal input terminals and the signal output terminals. As a result, it is possible to prevent the damage to the electromagnetic wave detecting device by the electric discharge and to increase reliability of the electromagnetic wave detecting device.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.